While magnetic recording of information is enormously successful, it has been found that in the prior art there is a limitation with respect to recording density. In the present state of the art the popular method of magnetic recording has been longitudinal recording. Magnetic recording systems to date generally recognize recorded bits of information by detecting pulse peaks within certain timing windows. Unfortunately systems often inadvertently shift pulse patterns, in time, with respect to the timing of the windows and this of course results in errors. It follows that when linear density is increased, the time windows in which the peak must be detected necessarily narrows and the systems become more sensitive to noise and there are resulting errors.
Magnetic recording techniques have turned to considering vertical recording as compared to longitudinal recording as a means for vastly improving the linear density of recorded information. Vertical magnetic recording has been accomplished by having the recording medium pass between two mirror image recording heads. The magnetic flux from a first recording head passes vertically from a first write tip through the magnetic recording medium to a second write tip (the write tip of a second recording head). The shape of the tips concentrate the flux and hence effect a magnetic polarization within the recording medium to provide recorded information. The magnetic flux having passed through the second tip is routed upstream to a flux return path of the second write head. The flux return head is designed to have a face which is many times larger than the write tip so that the flux passing into the flux return head is disbursed therealong and hence the flux density is low. The low density flux passes through the recording medium, upstream, to the flux return path of the first magnetic write head and therealong to complete a magnetic flux circuit. Because the density of the flux passing through the recording medium upstream is low, there is very little effect by way of reversing or weakening any patterns in the recording medium upstream.
In the prior art vertical recording technique there has been a prerequisite in that there has been required a relatively large distance between the write tip and the flux return path to prevent leakage flux cross-over. In other words in such techniques the full strength of the write flux is desired to effect a desired recording. However in such arrangements, as the described in U.S. Pat. No. 4,317,148 the downstream fringing flux, which is ignored, acts to reverse or weaken, the magnetic polarity of information having been previously recorded and to compensate therefor, the packing density has had to be reduced.
The present device employs a two layered recording medium, places the flux return section downstream and by specifically locating the write tip close to the flux return path, uses the flux return path as a magnetic shield to intercept downstream fringing flux and thus prevent reversal or weakening, of the magnetic polarity at the trailing edge of a recorded bit of information. As mentioned above the prior art is exemplified by the structure described in U.S. Pat. No. 4,317,148.